Melt the butter in a large pot on medium heat.
Stir in the cheese and continue to stir until melted.
Add the sour cream or yogurt and half of bread crumbs to cheese/butter mixture.
Blend well and mix with green beans.
Place in 1 1/2 qt. casserole dish that is lightly greased.
Sprinkle with remaining bread crumbs.
Bake at 350F for 30 minutes.